Re: [boost] [system] The new Boost.System is now ready

Subject: Re: [boost] [system] The new Boost.System is now ready
From: Peter Dimov (lists_at_[hidden])
Date: 2018-10-07 23:37:28

Gavin Lambert wrote:

> Also, in P1197R0, perhaps I'm missing some context (not having a copy of 
> the standard handy) but it seems peculiar that the Effects of the two new 
> message() overloads are ordered differently with respect to possibly 
> returning a literal message pointer, ignoring buffer and len.  Why is it 
> that the second can do this but not the first?

The first specification ([syserr.errcat.virtuals]) describes the default 
implementation in error_category. This exists for backward compatibility. 
Since user-defined categories that only override the current `message` 
already exist, if the make the new overload pure, we'll break them. So we 
supply a default that calls the string overload and copies the string into 
the buffer.

Since we have no idea what the returned string is, we can't return a literal 
under any circumstances. (Except on exception.)

The second specification ([syserr.errcat.derived]) describes what classes 
derived from error_category need to do.